1. Field of Invention
The invention relates to methods and systems that tunably delay an optical signal.
2. Description of Related Art
As optical fibers are becoming more and more ubiquitous in the optical communications community, the effects of polarization mode dispersion (PMD) caused by subtle defects of these optical fibers become increasingly important. Generally, PMD occurs when an optical signal propagates through a birefringent optical fiber causing various components of the optical signal to travel at varying velocities, thus causing a dispersion of an optical signal into multiple xe2x80x9cimagesxe2x80x9d.
It is well known that PMD can be compensated for by splitting the multiple images and re-aligning the images into a single coherent optical signal. Generally, such compensation devices are formed by combining a polarization controller with an appropriately designed delay line. Unfortunately, both polarization controllers and delay lines are often unwieldly in size, difficult to tune and may be very expensive to manufacture or maintain. Therefore, there is a need to provide new methods and systems to compensate for PMD.
The invention provides methods and systems for tunable delay lines suitable for larger PMD compensation devices. Particularly, the invention provides compact and inexpensive micro-machined tunable delay lines using adjustable micro-mirrors to tunably alter a path length traversed by an optical signal.
The combination of a polarization-state controller and the tunable delay line enables the components of a PMD-affected optical signal to be appropriately manipulated to compensate for PMD effects. For example, a dispersed optical signal, after having its polarization-state suitably altered, can be split into its fast and slow components. The fast component can then be delayed relative to the slow component, by controllably manipulating its path length via one or more adjustable micro-machined micro-mirrors. After appropriately delaying the fast component, the delayed fast component is combined with the slow component to provide an optical signal whose slow and fast components are substantially re-aligned with each other. Thus, the dispersing effects of PMD can be significantly compensated for.
Other features and advantages of the present invention are described below and are apparent from the accompanying drawings and from the detailed description which follows.